The present invention relates generally to a gas-insulated electric apparatus and a method of assembly thereof, or more in particular to a gas-insulated electric apparatus and a method of assembly thereof which has a construction suitable for preventing the decrease in the dielectric strength thereof ever in the case where conductive particles have intruded into or have been produced in the apparatus.
A gas-insulated electric apparatus is often constructed of a high-voltage structure member making up a conductor arranged in a metallic tubular member hermetically sealed with a electro-negative gas such as SF.sub.6 gas. Should a conductive particle intrude into this apparatus and sink and stay on the bottom of the tubular member, the conductive particle rises up from the interior surface of the tubular member independence on the electric field in the tubular member and floats in the gas space. This floating conductive particle extremely reduces the dielectric strength of the gas space. In order to secure the reliable insulation characteristic of the apparatus, it is desirable to construct an apparatus capable of protecting itself from the effect of the conductive particle.
Various apparatuses intended to obviate this problem have so far been conceived, in which an electrode of low electric field intensity is arranged on that part of the bottom of the tubular member where conductive particles fall and stay so that the particles may be caught in the electrode of low electric field intensity. In the case where the apparatus is arranged slantwise or is subjected to mechanical vibrations, however, the particle is liable to drift from the electrode of low electric field intensity and may be exposed to the parts of high electric field intensity again.
In order to obviate this problem, a conventional apparatus has been proposed, as disclosed in Japanese Patent Application Laid-Open No. 136811/80, in which an insulating layer of high dielectric constant is formed on the interior surface of the tubular member whereby the voltage applied to the apparatus gives rise to an electrostatic attraction force sufficiently strong to resist the electrostatic buoyancy acting on the conductive particle, thereby dampening the floating motion of the conductive particle. Such an apparatus requires an insulating layer formed of a material of high dielectric constant whose specific dielectric constant is higher than a predetermined value. A ferroelectric material mainly comprising a ferroelectric substance such as BaTiO.sub.3 is often used as the material making up the insulating layer of high dielectric constant. Such a ferroelectric material, however, is considerably expensive, and the cost thereof may account for a considerable portion of the total cost of an apparatus which requires the insulating layer over a wide area.